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Copyright © 2012 Pearson Education, Inc.
8C H A P T E R
Nutrients Involved inNutrients Involved inAntioxidant FunctionAntioxidant Function
and In Depthand In Depth
© 2012 Pearson Education, Inc.
What Are Antioxidants?
Antioxidants: chemicals that protect cells from damage from oxidation, including the following nutrients
Vitamin E Vitamin C Beta-carotene Vitamin A Selenium
PLAYPLAY Antioxidants
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Structure of Atoms
Atom: the smallest unit of matter Atoms are composed of
Nucleus—positively charged center portion of the atom
Electrons—negatively charged particles surrounding the nucleus
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Structure of Atoms
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Oxidation
Molecules are composed of atoms
During metabolic reactions, electrons can be transferred
From the atoms of one molecule To the atoms of another molecule
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Oxidation: The Exchange Function
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Oxidation
Oxidation: the loss of electrons from a molecule
Reduction: the gain of electrons by a molecule
Oxidation and reduction usually occur together as an exchange reaction
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Oxidation
Stable atoms contain an even number of paired electrons
Free radical: an atom that has lost an electron and is left with an unpaired electron
Free radicals are highly reactive and can cause damage to molecules in the cell
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Oxidation
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Oxidation
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Formation of Free Radicals
Many metabolic processes involve oxidation reactions and can produce free radicals
Free radicals are also produced by Pollution Ultraviolet light and radiation Toxic substances
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Impact of Free Radicals
Free radicals cause damage to Cell membranes Low-density lipoproteins (LDLs) Proteins in the cell Genetic material (DNA)
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Diseases Linked to Free Radicals
Cancer Heart disease Diabetes Arthritis
Cataracts Kidney disease Alzheimer’s disease Parkinson’s disease
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Antioxidants
Antioxidants can function in different ways Some vitamins donate their electrons to free
radicals to stabilize them Some minerals act with complex enzyme systems
to destroy free radicals Superoxide dismutase Catalase Glutathione peroxidase
PLAYPLAY Free Radical Formation
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Vitamin E
Vitamin E is a fat-soluble vitamin made of Tocotrienol—biologically inactive form Tocopherol—biologically active form
Functions of Vitamin E Primary role is as an antioxidant Protects polyunsaturated fatty acids (PUFAs) Protects low-density lipoproteins (LDLs)
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Vitamin E
Recommended Dietary Allowance (RDA) is 15 mg alpha-tocopherol per day
Tolerable upper limit (UL) is 1,000 mg per day
Sources of Vitamin E Vegetable oils, nuts, seeds, wheat germ, soybeans Animal and dairy products are poor sources
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Vitamin E
What if you consume too much vitamin E? Some studies suggest possible links to vascular
disease, diabetes, or heart failure at high doses over long periods; results are still unconfirmed
Common side effects such as nausea and diarrhea
Vitamin E can interfere with anticoagulant medications
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Vitamin E
What if you don’t consume enough vitamin E? Vitamin E deficiencies are uncommon Can result in fragile red blood cells (erythrocyte
hemolysis)
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Vitamin C
Vitamin C is a water-soluble vitamin that must be consumed in the human diet
Functions of Vitamin C Antioxidant Synthesis of collagen Prevents the disease scurvy Enhances the immune system Enhances the absorption of iron
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Vitamin C
Recommended intake 90 mg/day for men; 75 mg/day for women Smokers need an extra 35 mg/day UL is 2,000 mg/day for adults
Sources of vitamin C Fresh fruits and vegetables Heat destroys vitamin C Cooking foods lowers their vitamin C content
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Vitamin C
What if you consume too much vitamin C? Megadoses (ten times or more of the recommended
intake) of vitamin C can cause nausea, diarrhea, nosebleeds, and abdominal cramps
Can cause iron toxicity in people with hemochromatosis
Can lead to kidney stone formation in people with kidney disease
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Vitamin C
What if you don’t consume enough vitamin C? Scurvy: the most common vitamin C deficiency
disease Bleeding gums, loose teeth, weakness Can occur after one month of a diet deficient in
vitamin C
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Beta-Carotene
Beta-carotene is In the class of chemicals called carotenoids A provitamin: inactive precursors that must be
converted to the active form of a vitamin in the body
The precursor of retinol
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Beta-Carotene
Functions of beta-carotene A weak antioxidant Effective against oxidation in cell membranes and
LDLs
Carotenoids in general are known to Enhance the immune system Protect skin from damage by UV light Protect eyes from damage
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Beta-Carotene
Recommended intake Beta-carotene is not considered an essential
nutrient No Dietary Reference Intake (DRI) or RDA has
been established
Sources of beta-carotene Fruits and vegetables that are red, orange, yellow,
and deep green
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Beta-Carotene
What if you consume too much beta-carotene? Large quantities do not appear to be toxic Skin may turn yellow or orange at high intakes;
harmless and reversible
What if you don’t consume enough beta-carotene? There are no known deficiency symptoms
© 2012 Pearson Education, Inc.
Vitamin A
Vitamin A is a fat-soluble vitamin Excess vitamin A is stored in the liver, adipose
tissue, kidneys, and lungs There are three active forms of vitamin A
Retinol Retinal Retinoic acid
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Vitamin A
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Vitamin A
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Vitamin A
Functions of vitamin A Essential to proper vision Antioxidant, protecting LDL cholesterol Cell differentiation: the process by which cells
mature and specialize Sperm production and fertilization Bone growth
PLAYPLAY Vitamin A and the Visual Cycle
PLAYPLAY Vitamin A and Epithelial Tissue
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Vitamin A
Recommended intake RDA is 900 g/day for men, 700 g/day for
women
Sources of vitamin A Animal sources: liver, eggs Plant sources such as the provitamin carotenoids
(dark-green, orange, and deep-yellow fruits and vegetables)
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Vitamin A
What if you consume too much vitamin A? Vitamin A is highly toxic, especially from
supplements Birth defects and permanent damage to the liver
and eyes can result
What if you don’t consume enough vitamin A? Night blindness is the most common disease of
vitamin A deficiency Irreversible blindness (xerophthalmia)
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Selenium
Selenium is a trace mineral found in a few amino acids in the body
Functions of selenium Antioxidant—part of the glutathione peroxidase
enzyme system Production of thyroxine, a thyroid hormone
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Selenium
Recommended intake 55 g/day for men and women UL is 400 g/day
Sources of selenium Rich sources include organ meats, pork, seafood,
nuts, wheat, and rice
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Selenium
What if you consume too much selenium? Selenium toxicity (brittle hair, nails, skin rashes)
can result from supplements
What if you don’t consume enough selenium? Keshan disease: a form of heart disease Kashin-Beck disease: a type of arthritis
© 2012 Pearson Education, Inc.
Additional Antioxidants
Cofactor: a compound needed for proper functioning of an enzyme
Copper, zinc, and manganese are cofactors for the superoxide dismutase enzyme antioxidant system
Iron is a cofactor for the catalase antioxidant system
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In Depth: Cancer
Cancer: a group of related diseases characterized by cells growing out of control
Composed of three steps Initiation—a cell’s DNA is mutated Promotion—altered cell repeatedly divides Progression—cells grow out of control
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In Depth: Cancer
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In Depth: Cancer
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In Depth: Cancer
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In Depth: Cancer
Factors that increase cancer risk include Tobacco use Weight, diet, and physical activity level Infectious agents (e.g., STDs) Sun exposure (ultraviolet radiation) Environmental/occupational exposure
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Signs and Symptoms of Cancer
■ Unexplained weight loss
■ Fever
■ Extreme fatigue
■ Pain
■ Skin changes
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Signs and Symptoms of Cancer
■ Changes in bowel or bladder function
■ Indigestion or problems swallowing
■ Unusual bleeding or discharge
■ Skin thickenings or lumps
■ Nagging cough or hoarseness
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Cancer Treatments
■ Depends on stage at which cancer is found
■ Three major types of treatments:
■ Surgery
■ Radiation
■ Chemotherapy
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Cancer Prevention
■ Check: get screenings and exams
■ Quit: stop smoking and alcohol abuse
■ Move: get regular physical activity
■ Nourish: maintain a recommended weight and eat a balanced, healthful diet
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Role of Antioxidants in Cancer
Antioxidants may contribute to reducing the risk of cancer
Antioxidants may reduce cancer risk by Enhancing the immune system Inhibiting the growth of cancer cells Preventing oxidation damage to cells
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